Microsoft began disabling Exchange Web Services (EWS) in Exchange Online by default on 1 October 2026 — the start of a phased retirement it first announced in 2023 and which is scheduled to complete by 1 April 2027.
EWS is a long-standing API that third-party mail and calendar clients use to talk to Exchange Online. Microsoft is steering everyone to its modern Graph API, but migration is not automatic, and organisations with active EWS applications have been told to inventory and migrate them. Administrators can extend the cut-off to 31 March 2027, but that is a delay, not an exemption.
The most visible casualty is Apple's own software. macOS Mail and Calendar still connect to Exchange accounts using EWS, and there is no clean Graph migration path for users to take themselves — the client has to change, not the account. Until Apple updates or users move to Outlook, some Exchange-hosted mail accounts on the Mac may stop syncing, and calendar entries may stop updating. Enterprise IT departments have spent months warning staff and pushing them to Outlook, which uses a supported connection.
The wider lesson is familiar to anyone who has lived through an API sunset: the deadline is the easy part. The hard part is the long tail of clients — especially built-in ones bundled with an operating system — that quietly depend on the interface being retired. Microsoft's own timeline has run for more than three years; the fallout will be measured in the weeks after the switch, when users notice a mailbox that has quietly gone silent.
